In the treatment of cancer it is important to consider the induction of terminal differentiation as a means of reducing the number of malignant cells. B16/C3 melanoma cells provide an excellent in vitro model for studying this process. The major objective of this proposal then is to characterize the biochemical events leading to terminal differentiation in B16/C3 cells. A convenient marker for studying terminal differentiation in B16/C3 cells is the production of the pigment melanin. It is during the period of melanin production (melanization) that the cells terminally differentiate, that is loose their capacity for cell division. It is this property that one would like to induce during chemotherapeutic treatment. We have established that two chemotherapeutic agents, 5-fluouracil (FU) and cytochalasin B (CB) are potent inducers of terminal differentiation in B16/C3 cells. Differentiation of these cells occurs by a sequence which includes increases in intracellular cAMP, a rise in tyrosinase activity, induction of differentiation specific tyrosinase, increased tyrosine utilization, followed by melanin biosynthesis and cell death. We will characterize these events in B16/C3 cells and determine the points at which CB and FU act. We will also determine if there is a correlation between the accumulation of potentially toxic tyrosine metabolites and terminal differentiation. B16/C3 cells form tumors when injected into syngeneic mice. Tumors contain both undifferentiated and differentiated cells. Undifferentiated cells maintain the growth of the tumor whereas the differentiated cells do not proliferate. The results of our cell culture work will provide a basis for the use of CB and FU in vivo. We will determine if antitumor effects of CB and FU correlate with the appearance of differentiation specific markers in these tumors. The results of this work may suggest new approaches for the treatment of melanoma.